(1) Field of the Invention
The present invention relates to a diversity reception apparatus which uses two or more antennas to improve the reception quality. In particular, the present invention relates to a diversity reception apparatus which receives analog modulated signals.
(2) Description of the Related Art
Conventionally a diversity reception apparatus has been widely used regardless of broadcast and communication, the diversity reception apparatus using two or more antennas and attempting to improve the reception quality. And, the usefulness of such diversity reception apparatus is widely known.
On the other hand, there is a universal problem with the diversity reception apparatus. The diversity reception apparatus must have a plurality of reception processing systems associated with the plurality of antennas. In particular, a diversity reception apparatus called phase composing diversity has a complex configuration, adjusting each phase of signals received respectively by a plurality of antennas and additively synthesizing the signals. Thus, there is a problem that the implementation cost is substantial.
Also, in the case where later described demodulation processing is realized using digital method, there is a significant problem that a plurality of analog/digital conversion units (hereinafter, referred to as AD conversion unit) are required, but the AD conversion unit is expensive for a single component, and occupies a large space when incorporated in a Large Scale Integration (LSI) chip.
Conventionally, there have been suggested various solutions for the above mentioned problems. For example, Japanese Laid-Open Patent application No. 05-175942 discloses realizing synthetic diversity processing using a simple configuration which includes (i) a means for executing switching processing with an interval that is half a symbol period and (ii) only one AD conversion unit that has been conventionally required as many as two or more in a diversity reception apparatus which receives digital demodulated signal waves having relatively long symbol lengths.
In addition, Japanese Laid-Open Patent application No. 2001-267988 discloses a well-known technique executed by a diversity reception apparatus which receives analog modulated signals, the diversity reception apparatus having a configuration in which (i) a phase adjustment processing is executed, using a phase shifter, by executing analog processing on one or all of signals received by a plurality of antennas, (ii) the one or all of signals are additively composed and (iii) the composed signals are outputted to a demodulation processing unit executing analog or digital processing.
However, in such conventional diversity reception apparatus as described above, according to the technique disclosed in the Japanese Laid-Open Patent application No. 05-175942, the signal in the symbol period which is a relatively long time is fixed to a constant pattern, using a characteristic of a digital modulation method. Thereby, there is a problem that the above mentioned technique can only be applied to a diversity reception apparatus which receives digital modulated signals, and cannot be applied to a diversity reception apparatus which receives analog modulated signal.
On the other hand, in the case where phase composition is executed by analog processing such as the technique disclosed in the Japanese Laid-Open Patent application No. 2001-267988, there is a problem in implementation cost that control by analog signal is required, therefore a component of high precision is required, and adjustment after implementation is required.
An object of the present invention, in view of the above mentioned problems, is to provide a diversity reception apparatus executing phase composition using a digital method, which (i) can be realized by a simple configuration that only requires one AD conversion unit and (ii) can be applied to receiving analog modulated signals.